1. Field of the Invention
This invention relates in general to electronically steered, two-dimensional, conformal, phased array antennae, and in particular to such antennae having two-dimensional, subsurface, traveling-wave excitation.
2. Description of Related Art
The related art in the field of electronically-large phased arrays has primarily involved electrically-large two-dimensional traveling wave arrays with electronic beam steering in two planes having endfire beams. Such arrays are necessarily very densely populated and include many hundreds, if not thousands, of elements, particularly at K.sub.u band. Further, wraparound conformal array configurations, physically extending 360.degree. around the airframe axis become possible and desirable on cylindrical airframes, to achieve a full hemispherical beam steering coverage (forward hemisphere), or better yet, nearly full spherical coverage including all the forward and most of the backward hemisphere. Attaining such wide beam steering coverage makes many simultaneous operations possible, including wide-volume high-speed target search, multiple target tracking, proximity fuzing, terrain following, and ski skimming. Wide off-airframe-axis beam-steering close to the airframe roll plane is actually easier to obtain from cylindrical arrays than are endfire beams as it corresponds to broadside radiation for most of the array elements.
A two-dimensional traveling-wave array radiating an endfire beam, planar or conformal, is somewhat equivalent to an array of Yagi-Uda arrays. This analogy shows the relevance of some very recent work on the concept of supergain arrays. Indeed, supergain or quasi-supergain array designs are being considered as a viable and promising concept for seeker antenna applications. Investigators have shown that supergain performance is practical even in the case of cylindrical array radiating a broadside beam.
The innovative phased array teachings disclosed herein greatly reduce system complexity, volume and weight as well as development and production costs and make electronically-steered conformal phased arrays practical and affordable in smaller carrier airframes. These teachings also permit higher production yields, higher reliability and readiness in all applications, and greatly simplify logistical problems.
The inventive concepts include a new feed network configuration that can be designed to physically fit and perform a load bearing structural function within a very small internal depth below the external surface of a missile or other airframe. The new array-excitation method vastly reduces the requisite number of primary array feeding lines and control elements, particularly when frequency scanning can be used in one of the two beam-steering planes. The new pattern synthesis method provides the more rigorous and experimentally verifiable way of determining the required aperture distributions than is available in the prior art. The broadband capabilities of the tightly coupled delay structures serve to relax fabrication tolerance problems and make feasible many difficult broadband array applications. Finally, the new active array architecture eliminates the need for combining Transmit and Receive (T/R) functions into complex T/R modules and for using one such module to feed every array element.
The drastically reduced complexity of the new array configurations greatly increases the inner airframe space available for competing on-board payloads such as target identification processors, sophisticated guidance controls, proximity fuzes, auxiliary infrared seekers for dual-mode guidance, larger warheads, and more powerful and longer range propulsion systems.
These operational and technical benefits while eliminating all delicate moving parts and solving the conflicting technical problems typical of dual-mode Millimeter Wave/Infrared (MMW/IR) seeker systems.
Other advantages and attributes are readily discernible from this disclosure. The foregoing unresolved problems and deficiencies are clearly felt in the art and are solved by the invention in the manner described below.